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LCA? Well-to-wheels (WtW)? Carbon handprint? Sustainable transport jargon explained

The world of sustainable mobility is riding on the cutting-edge of technology and new rapid advancements often come with a unique, often confusing, terminology. The following will provide much-needed clarity on a number of commonly used concepts and terms to help navigate the complex lexicon of the burgeoning industry.

Chris Stokel-Walker, author, speaker and journalist

Chris Stokel-Walker


The world of sustainable mobility is driven by a wide range of new, innovative technologies tailored to extract the most out of renewable or otherwise environmentally friendly sources of energy. However, new technologies and inventions often come with a plethora of complicated terms.

These seemingly complicated terms exist to communicate how sustainable transport is changing and greatly improving societies around the world. Conveying the importance of sustainable transport solutions is vital in order to convince governments, policymakers and companies to follow on the path of sustainability.

“The terms are used, but they can be difficult to understand clearly and therefore require further explanation,” says Petri Lehmus, Vice President, Research and Development (R&D) at Neste, an expert in leading teams that create circular and renewable solutions for the economy and society.

Those who struggle to differentiate between carbon handprint and carbon footprint, or grapple with the concept of life cycle assessment, the following is meant to clarify and contextualize a number of commonly used - but rarely understood - concepts.

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Life cycle assessment (LCA)

Life cycle assessment (LCA) is a term omnipresent in all things sustainable transportation and mobility. 

But what does the term actually mean and how does its use differ when applied to fuel or vehicles?

Simply put, LCA is used to look at everything that goes into making a product; from vehicle manufacturing or fuel production, to all the materials used in the process - such as energy and transportation steps - and their ongoing environmental impact.

“When you buy a car, life cycle assessment looks at not only the narrow little bit about ownership and use, but what the entire process of the manufacturing and disposing of it looks like,” says Gordon Telling, Director of Policy at Sustainable Freight Solutions, a transport consultancy. 

Another factor is the energy used to fuel a car, which introduces another aspect to the life cycle impact and helps compare different solutions of mobility as one.

While one’s ownership of a vehicle may last only a few years, far more time and effort goes into making it, and, of course, disposing of it, which also has an impact on the environment. The same applies to the selection of the car’s energy source, which ranges from conventional liquid fossil fuels to the more futuristic hydrogen cell technology. However, it’s not simply about tailpipe climate emissions, but the product’s holistic impact on the planet throughout the life cycle, hence the term life cycle assessment.

According to Lehmus, LCA is often described as a ‘cradle to grave approach’. 

“It’s a science in itself and there’s good international LCA standards as well as fuel sustainability regulations in Europe and North America, which apply life cycle assessment results as one criteria for proof of sustainability.

”To represent a product’s life cycle assessment in a comparable way, it is vital to follow commonly agreed rules and regulations.

Well-to-wheels (WtW)

Transport and its impact on the climate though greenhouse gas emissions such as carbon dioxide CO2, methane CH4 and nitrous oxide N2O, is generally considered significant. This is  why sustainable transport and greenhouse gas emission reductions are often discussed interchangeably. 

Luckily, we have appropriate terminology to add much-needed clarity into the conversation.

Well-to-wheels (WtW) is used to assess the LCA of fuels, including all phases of its life cycle - from the extraction of raw materials to their use.

There are two components to the well-to-wheels assessment: well-to-tank (WtT) and tank-to-wheels (TtW). 

WtT includes the fuel production phases, and TtW the use of fuel. Typically, the phases are divided between fuels and vehicles. 

The terms are a hot-button topic for politicians who struggle to determine whether the environmental impact of greenhouse gas emissions of different power sources should be measured with the well-to-wheels process, or only a part of it.  

This distinction matters as, for example, electric vehicles are often seen as not adding any greenhouse gas emissions to the atmosphere due to having zero  tank-to-wheels emissions. They do, however, have an impact on the environment when well-to-wheels emissions are totaled in the calculations, and when emissions from the production of the electricity used to power the engine are taken into account.

Understanding WtW and TtW

For every liter of consumed gasoline, approximately 2.4kg of carbon is released into the atmosphere as carbon dioxide. The figure of 2.4kg of carbon dioxide per liter of gasoline is the climate impact of the fuel when tank-to-wheels emissions are taken into account, i.e. the emissions resulting from the engine burning the fuel. 

This, however, is not the fuel’s full climate impact as it leaves out the GHG emissions from extraction of crude oil, refining, and transportation of both the fuel and its raw materials. These emissions, accumulated over the entire life cycle of the fuel, are taken into account in the well-to-wheels approach.

Measuring the emissions from the vehicle’s tailpipe alone does not provide the full picture of the fuel’s climate impact as it does not take into account the origin of the carbon. The climate impact of the fuel is determined by whether the emissions released into the atmosphere come from fossil or renewable sources.

While there are carbon emissions related to biofuel use, the emissions are not “additional” as they consist of carbon emissions from renewable sources that are released back into the atmosphere, thus creating a carbon cycle.

Carbon dioxide emissions from the use-phase of renewable diesel are considered to amount to zero as the amount of bio-based carbon dioxide released upon combustion equals the amount that renewable raw material absorbed in an earlier stage. 

This is different from fossil fuels that pump the carbon from underground storage and build up carbon dioxide in the atmosphere, and subsequently, speed up climate change. 

From the climate perspective, this is what really makes the difference as  well-to-wheels calculates the total climate impact. 

Carbon handprint

To fight climate change, we need to drastically scale down our carbon footprint. A product’s carbon footprint refers to the life cycle impact of a product or a service. But few of us are familiar with carbon handprint.

The carbon handprint is a rejoinder to the negative connotations of singling out one’s carbon footprint. Product’s carbon handprint is about comparing two equal products or services and their climate impact. The handprint applies to the one that can show a smaller carbon footprint. Carbon handprint equals the difference between the two options in their carbon footprints, measured in mass of CO2 equivalent. 

The handprint measures the amount individuals and businesses save by choosing the better one of available options, with the intention of encouraging, and ultimately, improving future behavior. It should therefore be viewed as a carrot, rather than a stick, to drive positive change. 

“As you go through your daily life, you can add up the carbon cost of everything you do, whether it’s the coffee you drink or the car you drive,” says Telling. “The carbon handprint looks at what you’re doing to reduce that.” 

Carbon handprint functions as a positive reevaluation of our impact on the environment and encourages proactive action, rather than reactive. 

Credits: Chris Stokel-Walker, author, speaker and journalist whose work has appeared in BBC News, The New York Times and WIRED UK.